首页 | 官方网站   微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1839篇
  免费   0篇
工业技术   1839篇
  2021年   2篇
  2020年   5篇
  2019年   2篇
  2018年   2篇
  2017年   1篇
  2016年   4篇
  2014年   2篇
  2013年   4篇
  2012年   7篇
  2011年   4篇
  2010年   3篇
  2009年   1篇
  2008年   3篇
  2007年   4篇
  2006年   3篇
  2005年   3篇
  2004年   1篇
  2003年   3篇
  2002年   1篇
  2001年   1篇
  1999年   55篇
  1998年   587篇
  1997年   303篇
  1996年   204篇
  1995年   85篇
  1994年   82篇
  1993年   103篇
  1992年   11篇
  1991年   31篇
  1990年   22篇
  1989年   23篇
  1988年   18篇
  1987年   23篇
  1986年   21篇
  1985年   27篇
  1984年   1篇
  1983年   5篇
  1982年   5篇
  1981年   8篇
  1980年   19篇
  1979年   1篇
  1978年   6篇
  1977年   39篇
  1976年   96篇
  1975年   5篇
  1970年   1篇
  1962年   1篇
  1955年   1篇
排序方式: 共有1839条查询结果,搜索用时 32 毫秒
81.
Inhalation of hypertonic saline stimulates mucociliary clearance (MCC) in healthy subjects and those with obstructive lung disease. We investigated the effect of inhaling the osmotic agent mannitol on MCC. We used a dry-powder preparation of mannitol British Pharmacopea (BP) which was encapsulated and delivered using a Dinkihaler. MCC was measured for 75 min in six asthmatic and six healthy subjects on two occasions before and after the mannitol inhalation or its control, using 99mTc-sulphur colloid and a gamma camera. The inhaled dose of mannitol was 267+/-171 mg (mean+/-SD) and 400 mg and the percentage fall in forced expiratory volume in one second (FEV1) was 22+/-3 and 4+/-2% in the asthmatic and healthy subjects, respectively. The total clearance in the whole right lung for the 60 min from the start of inhalation of mannitol was greater by 263+/-11.9% in the asthmatic and 18.1+/-4.9% in the healthy subjects compared to the control. The total clearance over 75 min was 54.7+/-9.6% and 33.6+/-9.4% on the mannitol and control day (p<0.002), respectively, in the asthmatic subjects and 40.5+/-7.1% and 24.8+/-7.8% (p<0.002) in the healthy subjects. In conclusion, inhalation of dry-powder mannitol increases mucociliary clearance in asthmatic and healthy subjects and may benefit patients with abnormal mucociliary clearance.  相似文献   
82.
BACKGROUND: It has been suggested that excessive formation of nitric oxide (NO) is responsible for the hyperdynamic circulation observed in portal hypertension. Substance P is a neuropeptide partly cleared by the liver and causes vasodilatation through the activation of the endothelial NO pathway. However, there are no previously published data concerning the plasma level of substance P in cirrhotic rats and its relationship to NO. METHODS: Plasma concentrations of substance P and nitrate/nitrite (an index of NO production) were determined in control rats and cirrhotic rats with or without ascites using an enzyme-linked immununosorbent assay and a colorimetric assay, respectively. In addition, systemic and portal hemodynamics were evaluated by a thermodilution technique and catheterization. RESULTS: Cirrhotic rats with and without ascites had a lower systemic vascular resistance (2.6 +/- 0.2 and 3.9 +/- 0.4 mmHg ml(-1) x min x 100 g body weight, respectively) and higher portal pressure (14.6 +/- 0.6 and 11.3 +/- 1.8 mmHg) than control rats (6.5 +/- 0.3 mmHg x ml(-1) x min x 100 g BW and 6.8 +/- 0.2 mmHg, respectively, P < 0.05), and cirrhotic rats with ascites had the lowest systemic vascular resistance. Plasma levels of nitrate/nitrite progressively increased in relation to the severity of liver dysfunction (control rats, 2.7 +/- 0.5 nmol/ml; cirrhotic rats without ascites, 5.6 +/- 1.3 nmol/ml; cirrhotic rats with ascites, 8.3 +/- 2.2 nmol/ml; P < 0.05). Cirrhotic rats with ascites displayed higher plasma values of substance P (57.7 +/- 5.9 pg/ml) than cirrhotic rats without ascites (37.9 +/- 3.1 pg/ml, P < 0.05) and control rats (30.1 +/- 1.0 pg/ml, P < 0.05). There was no significant difference in plasma substance P values between control rats and cirrhotic rats without ascites (P > 0.05). No correlation was found between plasma levels of substance P and nitrate/nitrite (r = 0.318, P > 0.05). CONCLUSIONS: Excessive formation of NO may be responsible, at least partly, for the hemodynamic derangements in cirrhosis. Although substance P may not participate in the initiation of a hyperdynamic circulation in cirrhosis, it may contribute to the maintenance of the hyperdynamic circulation observed in cirrhotic rats with ascites.  相似文献   
83.
An emerging body of research on the physical and sexual abuse of seriously mentally ill (SMI) women documents a high incidence and prevalence of victimization within this population. While causal links are not well understood, there is convergent evidence that victimization of SMI women is associated with increased symptom levels, HIV-related risk behaviors, and such comorbid conditions as homelessness and substance abuse. These abuse correlates may influence chronicity, service utilization patterns, and treatment alliance. This article reviews the research literature on the prevalence, symptomatic and behavioral correlates, and treatment of abuse among SMI women, particularly women with schizophrenia. Within each topic, we discuss relevant research findings, limitations of available studies, and key questions that remain unanswered. We also discuss mechanisms that may underlie the relationship between trauma and schizophrenia-spectrum disorders. We conclude by outlining directions for future research in this area.  相似文献   
84.
85.
Recent evidence on visual neglect suggests that each hemisphere maintains a retinotopically organized representation of the visual world contralateral to the current fixation point and that this representation is based not only on analysis of the current retinal input but, equally importantly, on information retrieved from memory. This idea predicts that unilateral damage to memory systems should produce a lateralized impairment of memory for the retinotopically contralateral visual world. To test this prediction we examined visual recognition memory performance in the left and right visual hemifields of patients who had undergone partial unilateral temporal lobe removals for the relief of epilepsy, either in the left hemisphere (n = 5) or the right (n = 5). The patients were given complex artificial scenes to remember, constructed of independent left and right halves, and were then tested for recognition of the left and the right halves separately. Stimuli were exposed tachistoscopically throughout and fixation was maintained on a central position. Patients made significantly more errors with half-scenes in the hemifield contralateral to their removal than in the ipsilateral hemifield, an increase of 50% in the error rate on average. The effect was seen equally in patients with left and right removals. This finding supports the idea that visual memory retrieval is retinotopically organized.  相似文献   
86.
87.
A 14-year-old girl developed a firm mass at the base of the tongue. Computed tomography indicated marked density suggesting either a foreign body or bony tissue. A thyroid scan confirmed the presence of a normally sized and positioned gland. The mass was removed in toto and found to be an osteoma. This is the first report of a case in which the diagnosis of this rare developmental lesion of the tongue was achieved preoperatively based on clinical and radiologic information. This experience should lead to greater awareness of this entity in the future. Recognition of this entity in the pediatric age group is especially useful in avoiding misdiagnosis of other, potentially more aggressive types of tongue mass lesions. Our case demonstrates that it is possible to detect this entity using computed tomography. The dense calcification is truly characteristic of the tumor and may be relied upon to exclude alternative soft tissue mass lesions. While other forms of osseous and cartilagenous neoplasms, such as extraskeletal osteosarcoma and chondrosarcoma, have been reported arising in the tongue, their malignant nature should otherwise be readily apparent. Osteoma of the tongue is the favored diagnosis when mature bone tissue is imaged at the base of the tongue.  相似文献   
88.
During the last decades a number of left ventricular assist devices has been used especially for patients resistant to pharmacologic treatment and to intraaortic balloon pump (IABP) support for left ventricular failure. A high stroke volume para-aortic counterpulsation device (PACD) has been developed utilizing the principle of the diastolic counterpulsation technique. In this study the hemodynamic effects of the valveless PACD were compared to those of the centrifugal blood pump (CBP) in nine dogs in acute experimental cardiogenic shock. Hemodynamic measurements were obtained at baseline with both devices off, PACD on and CBP off, or PACD off and CBP on. There was no difference in mean aortic pressure between PACD on (60.0 +/- 11.5 mmHg) and CBP on (69.0 +/- 26.8 mmHg). Similarly, there was no difference in left ventricular end-diastolic pressure with the PACD on (11.9 +/- 5.4 mmHg) versus the CBP on (9.9 +/- 5.2 mmHg) or the cardiac index with the PACD on (84 +/- 36 ml/kg/min) versus the CBP on (77 +/- 36 ml/kg/min). However, the left ventricular systolic pressure (55.0 +/- 19.0 with PACD versus 73.0 +/- 26.0 with CBP,p < 0.001), the tension time index (712 +/- 381 versus 1333 +/- 694,p < 0.01), and the double product (5629 +/- 2574 versus 7440 +/- 3294,p < 0.01) were significantly lower during assistance with the PACD than with the CBP. It was concluded that PACD is at least as effective as CBP for restoring hemodynamic status during acute experimental cardiogenic shock. Moreover, the PACD unloads the left ventricle more effectively than CBP, making it suitable for left ventricular mechanical support in cases with reversible myocardial damage.  相似文献   
89.
90.
M-mode, two-dimensional, and Doppler echocardiography were performed in 38 chronic renal failure (CRD) patients on conservative management, 35 patients on hemodialysis, and 36 matched controls. The controls were matched for age, sex, and comorbidities. The incidence of hypertension, left ventricular (LV) end diastolic volume, LV end systolic volume, and LV mass index were significantly higher in patients on hemodialysis compared to the controls. The LV parameters in the predialysis patients were not significantly different from the controls, except the LV end systolic internal dimensions were significantly higher in the CRF patients. Multiple regression analysis underscored the strong association between increase in LV mass index (LVMI) and hypertension. The diabetic patients with renal failure had large LV internal diameter and end diastolic volume compared to non-diabetics. Systolic function was well preserved even in hypertensive and diabetic patients with uremia. The incidence of diastolic dysfunction and asymmetrical septal hypertrophy were not significantly different in the three groups of patients.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司    京ICP备09084417号

京公网安备 11010802026262号